This invention relates to Power Take-Off (PTO) apparatus for use with a wave energy converter (WEC) and, in particular, to an improved PTO system employing reciprocating linear motion.
In general, WECs are devices which convert mechanical energy present in ocean waves to electrical energy or any other suitable form of energy. WECs may take many different forms. The present invention is highly suitable for use with WECs which convert the wave energy motion into a reciprocating motion which is substantially linear.
FIG. 1 shows a prior art WEC in which the PTO includes a hydraulic system for driving a generator/motor. The WEC shown in FIG. 1 includes two main components: a toroid-shaped float (1) and a cylindrical-shaped spar (2), with the float (1) being disposed around the spar (2). In this configuration, the float may be designed to be neutrally buoyant whereby its waterline is substantially centered at about halfway of its height. The hydrodynamic design of the system is such that the spar (2) remains substantially stationary, or at least its dynamic behavior is dominated by its inertia; while the float (1) substantially follows the motion of the waves (i.e., is generally in phase with the waves). In addition to the hydrodynamic design, the spar (2) may also be held stationary by being anchored to the sea bed (as shown in FIG. 1) or it may be held relatively stationary with the aid of a heave plate which is attached near the bottom of the spar (2).
The relative force and motion between the float (1) and spar (2) is converted into electrical energy by means of a PTO (10) connected between them. In FIG. 1, the PTO includes a hydraulic system including a motor coupled via a shaft to a generator to produce electrical energy. Due to the relatively low frequency of the waves, the corresponding electrical signals tend to be of low frequency which is very inefficient. To overcome this problem various gearing mechanisms may be introduced to increase the frequency of the electrical signals being produced. However, known gearing mechanisms tend to require substantial maintenance and replacement and tend to be inefficient and unreliable.
Other problems exist with known systems in the efficient and reliable conversion of wave energy into electrical energy.
It is an object of the present invention to overcome many of the known problems and to provide a PTO apparatus which can convert the relative force and motion of the float and spar into electrical energy in an efficient and reliable manner.